Endurance exercise training elicits physiological adaptations which increase the functional capacity of various organs. Older, physically well-trained "master" athletes tend to have a cardiovascular functional capacity (maximal oxygen consumption, V02max) which more closely approximates that of much younger individuals than that of their sedentary peers. They also have higher levels of high density lipoprotein (HDL) cholesterol, lower percent body fat and their tissues are more insulin sensitive than that of age-matched sedentary controls. The interrelationship of age and physical fitness to endocrine-metabolic function, (lipid profiles, lipid metabolism, glucose metabolic rates and insulin sensitivity), and cardiovascular function is being examined in healthy lean older men (greater than 60 yrs), free of detectable coronary artery disease and metabolic dysfunction, and who have a wide range (25-50+ ml/kg.min) of V02max. The specific role of training on metabolic and cardiovascular function will be determined by deconditioning highly trained individuals over a 3 mo period and conditioning sedentary and less active subjects over a 6-9 month period, such that both groups achieve a common level of V02 max. Endocrine-metabolic function studies include: 1) glucose tolerance, beta cell sensitivity, and insulin sensitivity, 2) lipoprotein metabolism and lipoprotein lipase activity, and 3) sympathoadrenal responses to cycle exercise, and to lower body negative pressure. Baseline fasting glucose and lipid profiles have been obtained on 83 participants. Seventy-eight subjects have had oral glucose tolerance tests, and 68 of the men qualified have undergone an initial treadmill screening test and maximal oxygen consumption (V02max) test, 59 have undergone a second V02max test and thallium scans, 8 have undergone hyperglycemic clamps with measurements of insulin receptor binding, 13 have undergone multigated cardiac blood pool scans and 13 have had HDL subfraction analysis with measurement of postheparin plasma lipoprotein lipase activity.